Apparatus for making perforated sheet material



APPARATUS FOR MAKING PERFORATED SHEET MATERIAL Filed May 9, 1956 J. E. MCKEEN May 2, 1961 3 Sheets-Sheet 1 JOE/5 A E. McKEE/V INVENTOR.

APPARATUS FOR MAKING PERFORATED SHEET MATERIAL Filed May 9, 1956 J. E. M KEEN May 2, 1961 3 Sheets-Sheet 2 JOSZ A E. MCZE'E/V INVENTOR.

United States Patent O APPARATUS FOR MAKING PERFORATE'D SHEET MATERIAL Filed May 9, 1956, Ser. No. 583,793

1 Claim. (Cl. 93-1) This invention relates to the manufacture of perforated sheet material and more particularly to an apparatus for electrically perforating a moving web of sheet material in accordance with a predetermined pattern, as well as for concurrently performing other operations on the web.

It is often desirable to perforate sheet material with minute openings of uniform size, spacing and without leaving burrs and rough edges or deforming the sheet stock at the rims of the openings. None of the various perforating methods heretofore proposed are satisfactory. Mechanical perforators employing a punch and die technique in common use for making large size perforations are entirely impractical for forming very small openings owing to the cost of constructing and maintaining the dies, the difliculties encountered in clearing the punchings from both the sheet and the punching equipment, and the limitation on the size of opening which can be punched to sizes many times larger than desired. Another method which is quite unsatisfactory for obvious reasons involves pricking the stock with sharp pointed members mounted on either a rotating or a reciprocating member. Such perforations not only tend to close, but the method of producing them deforms one surface of the stock outwardly which is oftentimes quite objectionable.

Still another distinctly different mode of perforating which has ofiered much hope involves using an electric spark to burn a hole through the sheet by disposing electrodes on its opposite sides. However, the results obtained by the numerous electrical perforating techniques which have been proposed are unsatisfactory due to great variations in hole size, uneven spacing between holes, charring and smudging in the areas near the holes, lack of suitable means for coordinating the formation of the arcs with the rate of web movement, and other conditions well known to those skilled in this art. One of the particularly vexatious problems has been the control of the spark in a manner to burn a new hole at a desired point rather than take a circuitous path through a hole formed previously even though the last hole is located some distancefrom theelectrodes. Thus it has been found quite impractical when using prior techniques to form electrically-perforations in close proximity to one another because of this pronounced tendency of the next spark to take an errant path through a previously formed opening. Attempts to overcome this problem by locating the electrodes closer to the sheet being perforated "resistance, embedding particles of electrically conductive material in the stock to induce the spark to take a path throughthe' particle rather than to one side of it, and

others. 'Noneof these proposals has been fruitful.

The present invention provides an apparatus for perforating metallic and .nonmetallic sheet material with minute openings in a predetermined pattern by the useof electric arcs and obviating the disadvantages of prior proposals, the electric arcs being accurately timed with respect to one another and with the speed of the moving sheet. Precise control of the path of the are between electrodes is achieved by replacing with substantially nonionized gas any ionized gas present in the vicinity of the electrodes or sheet material immediately following the collapse of one are and before the next are forms between the same electrodes. This expedient eliminates th possibility of the next are taking place through the pt foration last formed even though this necessitates a circuitous path for the are. Another feature of the invention is the use of the cyclic growth of potential across the pairs of electrodes to time the spacing between arcs. This involves generating a maximum voltage on each cycle somewhat greater than required to form an are through the sheet material being perforated and utilizing the formation of the arc to initiate its own extinction. Another important feature is the coordination of the arc timing means with the speed of the sheet material past the perforating electrodes in a manner to provide a desired spacing of the perforations in either a uniform or a nonuniform manner as may be suitable.

One of the present highly advantageous uses for sheet material perforated with the precision made possible by the present invention is in making paper tape for concealing the joints between plaques of plaster board in a building structure. In this application, the minute perforations permit entrapped air to escape while the tape is being applied to the wall board without allowing the bonding material to pass through, thereby preventing the formation of air bubbles beneath the tape, and providing a superior joint with less labor. The present invention provides a unique apparatus for forming simultaneously a plurality of strips of such tape from a wide web of paper stock, including not only the perforation of the several tapes, but the skiving of each tape edge before slitting the web into separate strips, as well as the scoring of the strips to facilitate the fitting of the finished product over corner joints. In a preferred embodiment of the invention, a web of suitable paper stock is pulled from a supply roll through the electrical perforator, past a skiver designed to excavate a wide V-shaped channel in the web between adjacent strips of the tape, past a scoring device for impressing a score along the longitudinal center of each strip, and past slitter means for substantially but not quite severing the web into strips along the shallow center of each skived channel, the rate at which the web is pulled being coordinated with the firing of the perforating electrodes to provide a desired spacing between perforations.

In view of the foregoing factors and conditions characteristic of perforating devices heretofore proposed, it is a primary object of this invention to provide an improved apparatus for perforating sheet material by an electric arc to provide a superior product more economically.

Another object of the invention is the provision of a technique for perforating sheet material with minute openings arranged in a predetermined pattern.

A further object is the provision of an improved apparatus for perforating a moving web of sheet material by electric arcs the timing of which is coordinated with the rate of movement of the web to provide a desired spacing of the perforations.

Another object of the invention is the provision of a new perforated paper product and an apparatus for making the product rapidly and inexpensively.

Additionally, it is an object of this invention to provide an. improved mode of skiving a wide web of m'ov-.

4 3 ing sheet material to form V-shaped channels longitudinally thereof, whereby said web is adapted to be severed into separate strips having skived edges extending therealong.

Still further object is the provision of a skiving mechanism for sheet material having a power-driyen cylindrical abrading wheel for 'skiving moving sheet material backed by a crowned idler wheel.

Another object of the invention is the provision of an improved skivin'g mechanism employing a cylindrical abrading roll and a plurality of individually adjustable crowned back-up idlers forholding a moving web of sheet material against the abrading roll in predetermined areas spaced axially along the roll,

A further object is the provision of an improved apparatus for electrically perforating sheet material including the removal of ionized gases immediately following the extinction of one are and before the formation of another arc between thesame electrodes.

Another object of the invention is the provision of an apparatus for processing a wide web of paper in a continuous manner to form a plurality of perforated, skived strips substantially slit apart but sufficiently joined together for uniform winding as a unitary web" on a take up roll.

These and. other more specific objects will appear upon reading the following specification and claim and upon considering in connection therewith the attached drawings to which they relate.

Referring now to the drawings. in which a preferred embodiment of the invention is illustrated:

' Figure 1 is a diagrammatic view of an apparatus incorporating the features of the invention and showing a web of paper being processed to provide a plurality of strips of perforated tape;

Figure 2 is a, fragmentary view in elevation of the skiver sub-assembly;

Figure 3 is a fragmentary sectional view of the skiver taken along the line 44' in Figure 2;

Figure 4 is a transverse sectional view of the web after processing and before final separation into separate strips of tape;

Figure 5 is a view in perspective of a section of finished tape; I Figure 6 is a graphic view of the voltage and current flowing in the perforator circuit, together with a representation of the'arc conditions between a pair of electrodes at diiferent periods of a half cycle;

Figure 7 is a vertical sectional view through the perforating electrodes; and

' Figure 8-is a diagrammatic representation of the positions of the electrodes relative to the paper web and showing the manner ofconnecting them in circuit with the power supply.

Referring to Figure 1, a Web 10 of high strength paper is shown as extending from a supply roll 11 mounted on a rotatable mandrel 12 horizontally past a number of processing stations arranged at spaced points along the apparatus constituting the present invention. It will be understood that the side frames and supporting bearings for the various shafts and mandrels have been omitted from the drawings in the interest of greater clarity and as. being within the skill of a mechanic. Although various arrangements well known in the art may be employed for feeding web '10 past the processing stations under uniform tension, a suitable feeding device, illustrated by way of example, comprises a tensioning roll 13 mounted on a shaft 14 and preferably having a resillent high-friction covering of rubber or the like. A prime mover 15 acts through variable reduction gearing 16, shaft 17 and endless power transmitting means 18 to driveroll 13 at any desired speed by means of either electric or mechanical control means of well known type. Acting to. hold web 10 tightly pressed against a major surface area of, rollv 13 are. a pair of gr ppin rolls 19, 19 which may be suitably spring biased against roll '13.

The processed web discharging from tension roll 13 may pass to a conventional re-wind mechanism or, as here shown, to a take-up mandrel 20 disconnectably coupled to a slip clutch 21 driven through belting means 22 by a motor 23. As will be recognized, clutch 21 and motor 23 merely serve to prevent slack in the, web discharging from feed roll 13 by coiling the processed paper neatly in a roll 24.

Referring now to the left-hand portion of Figure 1, it will be noted that the first processing station designated generally 25 is formed by a rectangular housing 26 having narrow slots 27, 27 arranged horizontally in its side walls and through which the tensioned web 10 of paper passes. The forward end wall of housing 26 is cut away to disclose features of the interior construction, there being a partition 28 extending substantially across the mid-portion of housing 26 to provide an air outlet 29 for supplying air to'a pair of plenum chambers 30, 31 divided from one another by paper web 10 and in free communication through a connecting air duct 32. A large volume of circulating air is assured by a blower 33 having an inlet duct 34 opening through the wall of housing 26 and discharging through outlet 35 over a plurality of high voltage transformers 36 suitably supported in the lower half of housing 26. Blower 33 may be separately driven by its own motor but, as here shown,

is driven from prime mover 15 through a pair of belt drives 37, 38, the latter of which belts passes through an opening 39 in housing 26. Belt 37 serves additionally as the drive means for an induction generator 40 having its output leads 41 connected to energize the primary coils 42 of transformers 36. Generator 40 is designed to have a substantially constant voltage but a frequency varying with its rotational speed as determined by the speed of the output shaft 17 of prime mover 15 for a purpose to be explained presently.

Rigidly mounted in plenum chambers 30, 31 on high voltage'insulator grids 45 (Figure 7) are a plurality of upper and lower electrodes 46 and, 47, respectively. These electrodes are arranged in aligned pairs with the tips of each pair closely spaced from the opposite sides of web 10, as is best shown in Figure 7, and each being frictionally retained in a desired axially adjusted position by grids 45. In a'preferred embodiment, the electrodes are arranged in groups transversely of web '10 in the manner diagrammatically indicated in Figure 8, with the electrodes in one group being offset in eschelon from those in another to form a desired, pattern of perforations. Lead wires 49 serve to connect each pair of electrodes in a given group in series with one another, with a suitable pulse-forming network 49' (Figure 8), and with the secondary 50 of one of the transformers 36. The pulse-forming network 49 may comprise a resistance, a linear reactor, a nonlinear reactor, or any suitable combination of these devices to limit the current flow when the are forms to the design load of the transformers. Only one transformer and one group of electrodes have been diagrammatically indicated in Figure 1, but it will be recognized that in the manufacture of multiple tapes for sealing plaster board joints, a plurality of electrode groups and transformers would be employed. As an example, excellent results are obtained by providing a voltage drop of 2500 volts across each pair of electrodes with six pairs arranged in series with a common transformer 36 of the well known current limiting type.

At the second processing station, designated generally 51, is performed the important skiving operation to provide shallow but wide V-shaped channels 52 extending lengthwise of web 10,, as is best illustrated in Figure 4. These channels are spaced such that the slitting of web 10 along their longitudinal centers severs the web into strips of tapev 54 approximately two inches wide and having the gradually sloping or feathered lateral edges indicated at 53 in Figure 5. Referring to Figures 1, 2 and 3, skiving station 51 will be seen to include a heavy duty shaft 55 having rigidly clamped thereto by nut 56 a plurality of coarse-grained cylindrical abrading wheels 57 spaced from one another by thin resilient spacer washers 58. Shaft 55 is driven at a suitable abrading speed by a motor and power transmission device 59, the direction of drive being indicated by an arrow in Figure l. Underlying shaft 55 and paper web is a back-up wheel assembly comprising an idler shaft 60 supporting a back-up wheel 61 centered beneath each abrading wheel 57, as is indicated in Figure 2. Each wheel 61 comprises a ball bearing assembly 62, the periphcry of the outer raceway of which is crowned at 63, the angle of crowning illustrated being greatly exaggerated for purposes of illustration. The inner periphery of each inner raceway is press fitted to an eccentric 64 rotatable through a limited arc on shaft 60 under the control of an adjustable lever 65 fixed to one face of the eccentric. The free ends of levers 65 have an elongated opening for receiving an adjusting cap screw 66 threaded into a stationary anchor member 67, compression springs 68' being mounted between levers 65 and member 67 to urge levers 65 against the heads of the cap screws. It will therefore be evident that the adjustment of levers 65 by screws 66 serves to rotate the eccentrics 64 to shift crowns 63 of the back-up wheels closer or farther from the surface of abrading wheels 57. It will be understood that the 1 lower surface of the abrading wheels is spaced somewhat above a plane through tensioned web 10 with the result that adjustment of the back-up wheels 61 toward abrader wheels 57 deflects into contact with the abraders only those narrow strips of the Web directly overlying the crowns 63. In consequence, the cylindrical surfaces of the abrader wheels are effective to form V-shaped channels in the web. The significance of this resides in the fact that readily available inexpensive abrading wheels can be used in contrast with the bevelled abraders which lose their shape in use and are extremely difiicult and costly to service. Should the abraders of the present construction require truing, this can be accomplished quickly and inexpensively without removing them from their installed positions.

Another feature found desirable in a sealing tape for plaster board is the provision of a longitudinal score indicated at 69 in Figures 4 and 5. These scores are formed by disks 70 mounted on a shaft 71 and having rounded edges pressing web 10 against a soft rubber back-up roll 72, there being one scoring disk for each strip of tape being formed from web 10.

The final processing station comprises a slitter 75 having a motor 76 connected to drive a shaft 77 on which are mounted disk slitter knives 78 having their sharp edges bearing against an idler back-up roll 79. A separate slitter disk is provided for each severance desired in web 10, these severances 80 normally being located in the shallow part of V-shaped channels 52, as is indicated in Figure 4. Preferably, and as shown, slits 80 do not fully penetrate the web, but leave an unsevered portion approximately 0.001 inch thick, obtainable by the proper control of the pressure between the slitter knives and the back-up roll in a manner well known to those skilled in the operation of rotating slitters. The described thin connecting elements serve to keep all strips of the web accurately positioned laterally as they pass through the drive rolls 13 and 19 and onto the take-up roll 24. In the absence of these connecting elements the completely severed strips have a marked tendency to interweave on the take-up roll, causing unequal tensioning of the strips and serious winding problems.

Operation In the operation of the apparatus described above, the paper web 10 is threaded through the several processing stations from the supply roll 11 mounted on mandrel 1 2 and its end is attached to take-up mandrel 20, the threading operation being performed in an obvious manner. Once threading has been accomplished, the variable speed gearing 16 driven by prime mover 15 is regulated to rotate tension roll 13 and induction generator 40 slowly until all parts are observed to be functioning properly, after which the speed of web 10 is increased to a desired operating value. Driving motors 23, 59 and 76 are started and the speeds thereof adjusted to values suitable for use with the selected speed of advance of web 10, it being understood that the web speed can be adjusted over a wide range without varying the characteristics of the resulting product in any respect. For example, the size and'spacing of the perforations in the tape remain the same regardless of the speed of the web over a range of 25 to 600 or 700 feet per minute, as is likewise true with respect to all other operations performed on the paper.

The manner in which electric perforator assembly 25 operates in conjunction with induction generator 40 and the common variable speed drive for the generator and the web will be explained by reference to Figure 6. Graphically illustrated at 86 is the trace of the cyclic voltage wave flowing through each secondary 50 and the associated group of electrodes 46, 47 in series circuit therewith. In contrast, dotted line 86 indicates the trace the voltage wave would form if an arc were not created between the electrodes. Thus it will be understood that the spacing of the electrodes is so selected in relation to the dielectric strength of web 10 and the impressed voltage that an are 87 forms at a potential somewhat below the peak value during each half cycle. Once are 87 is created toform a minute perforation 85, the voltage starts to decay abruptly as the short-circuit current flow represented graphically by trace 88 increases and then decays in advance of the decaying voltage wave. The nature of the current flow is an important feature of the invention and is determined by the design characteristics of the pulse-forming network 4-9 connected in circuit with the electrodes. This network functions to store energy until arcs form at the electrodes and then to release this energy abruptly, preferably as a sharp pulse limited in value and duration by the resistances and/or reactors not in excess of a safe operating load for transformers 36 in manners well known to those skilled in the art. Usually transformers of this type employ an air gap in the core structure, as well as a more massive core structure.

.The conditions prevailing between each pair ofelectrodes during different portions of a half cycle of the voltage wave are represented by the diagrams designated A, B, C, D and E in the upper left-hand corner of Figure 6. In diagram A no arc exists because the voltage has not reached an arc-forming potential. However, an instant later the voltage has reached a potentialof 2400 volts to create arc 87 piercing moving Web 10 as indicated in diagram B. As the web continues to move, arc 87 persists and takes the arched path indicated in diagram C. Occasionally the arc reaches such an over-extended position as that indicated in diagram D before failing. During the next half cycle the voltage increases with an opposite polarity until the same arc-forming potential is reached to pierce a new hole 85 through web 10 at a point directly between the electrodes and at a predetermined distance from the perforation made by the same pair of electrodes during the preceding half cycle of the voltage wave. It will be understood that the spacing between perforations in the direction of web travel is determined solely by the speed of the web and the frequency of the cyclic power supply provided by induction generator 40. Since the latter is driven by the same power source as is web 10, namely, prime mover 15, it follows that any variation in the speed of the web is accompanied by a corresponding change in the frequency of the power supply to transformers 36.

A most important role is served by blower 33 and the air circulated thereby in assuring the uniform spacing of perforations 85 and in preventing a new arc from taking a circuitous path through the last formed. perforation. This is accomplished by. maintaining a rapid fiow of substantially nonionized air over the'electrodes and across the opposite surfaces of the web adjacent the electrodes, the velocity of air flow being at least ten feet per second faster than the velocity of the web. Such a rapidly flowing air stream is effective in removing ionized gases and particles from the vicinity of the electrodes and from the last formed perforation before a new arc is struck, with the result that the new are forms along the shortest path between the electrodes. It will also be evident that the air serves additionally to cool the transformers, the electrodes and the paper web as it conducts heat and ionized gases from plenum chambers 30' and 31 through slots 27.

Referring to Figure 8, it will be observed that three groups of electrodes are shown, each including five pairs of uniformly spaced electrodes arranged in eschelon to perforate five strips of tape simultaneously. It will be apparentthat a lesser or greater number of strips can be perforated by an appropriate decrease or increase in the electrodes and in the transformer circuits.

After the web leaves perforator 25, it passes through skiver station 51 where the crowned portions 63 of backup Wheels 61 press the web against the cylindrical surface of the rapidly rotating abraders 57. Due to the action of crowns 63, the abraders are effective to cut V-shaped channels lengthwise of the web centrally between the grouped rows of perforations indicated at 52, 52 in Figure 4. The depth of channels 52 may be adjusted by turning cap screws 66 to shift levers 65 and the attached eccentric 64, thereby changing the position of the back-up wheels 61 relative to abraders 57.

The web. then passes between roller 72 and scoring disks 70 which are positioned to score the tape along the longitudinal center of each strip as is indicated at 69. This score line aids in folding the tape as it is applied to either inside or outside corners.

In the final processing operation the web passes through slitting knives 78 positioned substantially to sever the web into separate strips 54 at slits 80 extending along the shallowest portion of channels 52. At the same time, the edges 89 of the web are severed in readiness for discard as the strips of tape are separated and wound onto small spools. of a size convenient for merchandising. Since, as described above, slits 80 preferably do not completely penetrate the web, the individual strips 54, as Well as trim edges '89, remain connected together as the Webpasses through the web-driving rolls 13, 19 and onto. the final take-up roll 24. As a result, all strips remain in position and are prevented in this manner from coiling one upon another as is otherwise found to be inevitable.

While the invention has been described in connection with the electrical perforation of paper and more particularly the manufacture of paper tape for use in sealing joints of a specific type, it will be understood that the invention is suitable for a great variety of applications. Sheet materials of all kinds including metals, plasticsand nonmetallic materials can be perforated by the techniques and principles disclosed herein. Likewise, it will be recognized that the principles of the skiving and other subassemblies are applicable in various other environments as well as in combination with the several operations constituting features of the present invention.

I claim:

Apparatus for the dry processing of a rapidly moving wide web of paper into a plurality of similar weaklyjoined parallel strips of tape each skived along its lateral edges and having distributed thereover in a predetermined pattern substantially identical minute perforations, said apparatus comprising means supporting a roll of paper sufficiently wide to form the desired plural number of tape strips, power driven means including a single take-up arbor for passing said web past a perforating sta-' tion and a skiving station closely spaced from one another longitudinally of said web at a speed in excess of feet per minute while said web is maintained under longitudinal tension from said supply roll to said take-up arbor, said perforating station including a plurality of pairs of spark electrodes closely spaced to either side of said web and out of contact therewith for forming parallel rows of perforations longitudinally of said web, means energized. by alternating current for creating paper-perforating arcs between said pairs of electrodes and having an are life restricted to a fraction of each half cycle of the alternating current, means for dissipating the ionized gas between said pairs of electrodes between successive energizations of said electrodes to prevent a subsequent are from passing through the last formed perforation, means for concurrently grinding away parallel wide V- shaped channels lengthwise of said rapidly moving web of paper which channels are located between multiple rows of perforations spaced to either side of said channels, the bottoms, of said V-shaped channels being so thin as to hold the contiguous portions of said wide web joined together only weakly thereby to facilitate the smooth reel ing of the, processed web on said take-up arbor.

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